Update dev docs to reference the new skia debugger (skiaserve)

Update dev docs to reference the new skia debugger (skiaserve)

This patch adds a new markdown file describing the new debugger along
with instructions on running it locally and a sweet screenshot. The
screenshot has been sized to not be clipped when viewed in production.

The old documentation for the qt-based debugger has been marked as
deprecated and all docs referencing the old debugger have been updated.

BUG=skia:5493
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2121673002
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=2121673002

Review-Url: https://codereview.chromium.org/2121673002